raw: Probe required direct I/O alignment

Add a bs->request_alignment field that contains the required
offset/length alignment for I/O requests and fill it in the raw block
drivers. Use ioctls if possible, else see what alignment it takes for
O_DIRECT to succeed.

While at it, also expose the memory alignment requirements, which may be
(and in practice are) different from the disk alignment requirements.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/block.c b/block.c
index 195beff706..d4dd7fe172 100644
--- a/block.c
+++ b/block.c
@@ -852,6 +852,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     bs->open_flags = flags;
     bs->guest_block_size = 512;
+    bs->request_alignment = 512;
     bs->zero_beyond_eof = true;
     open_flags = bdrv_open_flags(bs, flags);
     bs->read_only = !(open_flags & BDRV_O_RDWR);
@@ -920,6 +921,8 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
     }
 
     bdrv_refresh_limits(bs);
+    assert(bdrv_opt_mem_align(bs) != 0);
+    assert(bs->request_alignment != 0);
 
 #ifndef _WIN32
     if (bs->is_temporary) {